Apple has laid to rest months of speculation by unveiling not one but two models of iPhone 6 – one larger than the other, but both significantly bigger than the existing device.

The company also launch the long-awaited Apple Watch, a wrist-mounted smart device that works in conjunction with the phone.

The iPhone 6 is just 6.9mm deep, making it the slimmest handset Apple has ever made. Its bigger brother, which will be called the iPhone 6 Plus, is 2mm thicker.

The new models look indistinguishable from the leaked photos and videos published widely in the past few weeks.

Here’s what we know so far about the iPhone 6:

It will come in two screen sizes, 4.7 inches for the iPhone 6 and 5.5 inches for the iPhone 6 Plus. That compares with the four-inch screen of the iPhone 5S.

The frame of the iPhone 6 will be 6.9mm thick, and the iPhone 6 Plus 7.1mm thick.

The design is a departure from recent models, with rounded sides replacing the sharp-edged, flat-sided iPhone 5S.

The iPhone 6 screen resolution will be 1,334×750 pixels, which Apple describes as Retina HD; the iPhone 6 Plus will feature a full HD resolution of 1,920×1,080 pixels

The screen will be protected by ion-strengthened glass (but not the much-discussed sapphire crystal)

The iPhone 6 has improved camera specs, with an eight megapixel sensor, a new focusing system and slow-motion video at 240 frames per second. The iPhone 6 Plus also has optical image stabilisation.

The larger screen on the Plus model will allow multi-tasking, allowing the user to see an email inbox and message at the same time, for example. The app dock can also be moved to the side of the screen, instead of the bottom.

As expected, the handsets will come a Health app that will integrate with Nike’s fitness app

They will also include a built-in barometer.

Both iPhones will be available from 19 September in the UK, but British prices are yet to be confirmed.

6.10pm: Tim Cook, Apple’s chief executive, arrives on stage a little late, but he breaks with company tradition and goes straight to the big news: Apple is launching two new phones, the iPhone 6 and iPhone 6 Plus. Cook’s predecessor, Steve Jobs, always started with routine announcements and saved the biggest unveiling until last.

iPhone 6: what to expect

9 September

As the world’s technology press descends on Cupertino, California, for the launch of the iPhone 6, the Apple rumour mill has gone into overdrive. In the year since the relatively low-key launch of the iPhone 5S and 5C, rumours have come and gone about the new specs and features likely to find their way into its successor.

While some of it seems to be based on wishful thinking, much is likely to prove well founded. Here is our round-up of the most frequently discussed iPhone 6 specs, and how likely they are to make it into production.

iPhone 6 launch date: Analysts are expecting two versions of the iPhone 6, but it is unclear whether both will make an appearance tonight. It’ll be a huge surprise if Apple doesn’t produce a 4.7-inch device, but some analysts also expect to see a larger, 5.5-inch handset. Others think that the bigger iPhone 6 will not appear until later in the year. It’s also unclear when the new phones will go on sale, but 19 September is the date most frequently predicted.

iPayments: Recent reports suggest that Apple is working on a mobile payments system that will be unveiled alongside the iPhone 6 on 9 September. “Apple has reached an agreement with American Express to work together on its new iPhone payments system,” Re/code reported, and Bloomberg later added that Visa and Mastercard have also signed up. The system is likely to use near field communication (NFC) technology, which transfers data to be transferred between a device and a reader when the two are held against each other. The iPhone 6 would therefore work in the same way as the contactless debit and credit cards which have recently entered circulation.

Sapphire crystal: the use of sapphire crystal (also known as sapphire glass) for the iPhone 6 screen has been one of the most persistent rumours about the new handset. Apple is known to have invested heavily in the super-strong manmade material, which is resistant to scratching and bending, but recent reports suggest that it has been having trouble making it in sufficient quantities – and at sufficiently low costs – to furnish an iPhone production run of 100 million units or more. The Guardian recently suggested that Apple may end up using a blend of glass and sapphire crystal.

A Liquidmetal shell: As Apple strives to make the new handset as slim and strong as possible, some commentators have speculated that it may turn to Liquidmetal, an alloy that’s stronger than aluminium. In theory that would mean the handset could be lighter and slimmer without skimping on strength or build quality, but in practice it seems unlikely. Although one of the inventors of Liquidmetal predicted two years ago that Liquidmetal cases would be possible by mid-2014, its use has so far been limited to small components.

Liquidmetal components: This is much more likely. Documents published by Apple-watching website MacRumors, suggest that the alloy could be used in buttons and switches in order to toughen up what have often proved to be weak points on previous iPhones.

Aluminium frame: Although Liquidmetal may be off the cards, most of the leaked images and technical drawings suggest that Apple will adopt an all-metal rear frame for the iPhone 6. Previous iPhones have made either extensive or decorative uses of glass, but this year’s preview shots appear to show a rear panel fashioned entirely from aluminium – with a cut-out for the Apple logo.

Super-slim frame: Whatever it’s made from, most commentators expect the iPhone 6 to be noticeably slimmer than its already svelte predecessor. A few months ago some were predicting a depth of just 6mm, but specs supposedly leaked by Amazon in recent weeks suggest we can look forward to a 7mm iPhone. The slender dimensions are apparently causing problems for component-makers: the difficulty of making a battery that’s just 2mm thick has reportedly led to production delays.

A8 chip: Concerted speculation that the new device would include a revamped processor has been “confirmed” by Venturebeat. “The A8 will run at a frequency of 2.0 GHz per core and will create noticeably faster response time and graphics rendering in the new phones,” its source says. “By comparison, the A7 chips in the iPhone 5 run at only 1.3GHz per core.” Even if those details prove wide of the mark, a newer, speedier chip is a safe bet: Apple is unlikely to build an all-new phone around old technology.

13-megapixel camera: There has been comparatively little speculation about the iPhone 6 camera, but tentative reports out today suggest that Apple may build in a 13-megapixels sensor capable of recording high-resolution 4K video. “Apple is well-known for investing millions into its camera sensor, though the company has always refrained from entering the megapixel count race because adding more megapixels tend to have an negative effect on the low-light performance,” Tech Times says. But the website sounds a note of caution: “The original source comes from a Chinese web forum, which may not be the best place to find legitimate iPhone 6 leaked information.”

Optical image stabilisation:MacRumors says the bigger of the two iPhone 6 models “may include camera improvements in the form of optical image stabilisation with modules produced by sensor company InvenSense”. Camera performance is becoming increasingly important at the top end of the smartphone market, and analysts suggest that optical stabilisation, which reduces image blur, could help to justify a larger price tag for the 5.5-inch iPhone 6.

A curved screen: At the end of last year Bloomberg carried a report predicting the next iPhone models would have screens that curved down at the edges. Curved screens are said to be more durable, more comfortable to use, and better suited to watching videos and playing games, according to Sky News. This would be a bold move for Apple, which usually likes to stand back and see how other phone-makers fare with new, risky technologies – and more recently a source told The Wall Street Journal that Apple has no plans to make use of curved glass. However, despite all the leaked images apparently showing the iPhone 6 with a flat screen, rumours of curved glass have resurfaced, most recently in the Daily Mirror.

Quantum dots: This is probably a technology for future handsets, not the iPhone 6. Patent filings suggest Apple is experimenting with tiny crystal semiconductors just a few thousandths of a millimetre across, which could improve the colour and sharpness of mobile screens. “The techniques Apple describes would let its screens not only show colours more accurately,” Business Insider says, “but also show a wider gamut of colours.” The publication had predicted in March that the quantum-dot screen may be ready this year, but no further reports of the technology have emerged.

Battery life: Mixed signals have emerged about the iPhone 6 battery life. On the positive side, analysts have pointed to iOS 8, Apple’s new operating system, and its new A8 processor as evidence that the company is paying more attention to power consumption. The chip, says 9to5Mac.com “adds significant performance and efficiency enhancements in order to improve the iPhone’s battery life”. On the other hand, more recent reports suggest that the slim frame of the new phone has forced Apple to adopt a battery that is just 2mm thick. Taiwanese sources suggest that the new battery has a “similar capacity” to its predecessor, which may dash hopes of significantly improved performance.

Eye-tracking: Some rumours suggested that the iPhone 5S would be eye-controlled, allowing users to scroll through pages without touching the device. When the technology failed to materialise in the last model, hopeful observers shifted their attention to the iPhone 6.

NFC: Another long-predicted feature, Near Field Communication or NFC would allow the phone to act as a payment system. Users would wave their handsets over a receiver to transfer money in shops and restaurants, or between friends. Several Android and Windows Phone devices already support NFC payments, but Apple has yet to make the leap.

Health monitors and apps: Apple has already unveiled its new operating system, iOS 8, and what we’ve seen so far suggests that Apple is turning its attention to health and fitness. Smartphone accessories such as the Fitbit and FuelBand have proven the demand for health-monitoring devices, and reports suggest that the iPhone 6 will be able to keep track of its owners pulse and body temperature, as well as other metrics. These features may work in conjunction with the long-awaited Apple iWatch.

Price: Financial analysts suggest that the iPhone 6 will be more expensive than its predecessors, in part because of the cost of new components, and in part to re-establish the profit margin eroded by last year’s upgrade. When Amazon Japan apparently leaked details of the new device last month, the price, which was the equivalent of £100 higher than a similar iPhone 5S model, took many commentators by surprise. It’s unclear whether the leak reflected genuine pricing information, or even if it was a way for Apple to test reaction to a price rise.

Production run: After relatively minor iPhone upgrades last year, analysts expect this year’s more substantial changes to create unprecedented demand. According to the Wall Street Journal, Apple “is asking suppliers to manufacture between 70 million and 80 million units combined of two large-screen iPhones with 4.7-inch and 5.5-inch displays by Dec. 30”. That’s substantially more than the 50 to 60 million iPhone 5S and 5C production run last year, and a huge leap from the 35.2 million iPhones sold in the three months to June.